Over 10 million tons of biosolids from municipal sewage sludge are generated each year in the United States alone. The prevailing methods for the disposal of biosolids biosolids include the application of the biosolids to surface land application, such as to crop land, range land or forests, composting and landfill disposal. Each of these methods is associated with disadvantages.
For example, one disadvantage of the application of biosolids to surface lands is the resistance of persons living in the area of the application because of concerns about nuisances such as odor and wind-blown dust from the site of application. Biosolids application to surface land and landfills also creates risks for contamination of potable surface water and groundwater.
Further disadvantageously, weather conditions can delay the application of biosolids to surface land, and trucking biosolids to the application site creates pollution and nuisances. Additionally, the capacity for the disposal of biosolids by application to surface lands and landfills is limited and the associated costs are generally high. Also, greenhouse gasses, such as methane and carbon dioxide, are generated by the decomposition of the biosolids and these gases are released into the atmosphere at the sites of surface land application and most landfills.
Therefore, there is a need for an additional method for the disposal of biosolids that provides less risk for environmental contamination. Additionally, there is a need for a additional method for the disposal of biosolids that is less expensive. Further, there is a need for an additional method for the disposal of biosolids that does not permit the release of carbon dioxide and other green house gases into the atmosphere. Also, there is a need for an additional method for the disposal of biosolids that can produce usable byproducts from biosolids.
According to one embodiment of the present invention, there is provided a method for the disposal of biosolids. The method comprises, first, providing a supply of biosolids. Then, a slurry of the biosolids suitable for injecting is created and an injection formation below a ground surface is selected. The injection formation comprises a natural gas formation in a gas accumulation zone. Next, the biosolids slurry is injected into the injection formation at a pressure sufficient to create and maintain fractures within the selected injection formation. Then, the injected biosolids slurry is allowed to degrade.
In a preferred embodiment, the supply of biosolids can be derived from at least one source selected from the group consisting of municipal sewage waste, waste water treatment waste, animal waste, non-human-non-animal industrial waste and a combination of the preceding. In another preferred embodiment, the injection formation is at least about 100 meters below the ground surface. In a particularly preferred embodiment, the injection formation is from between about 500 and about 3,000 meters below the ground surface.
In a preferred embodiment, the injection formation has a temperature and the temperature of the injection formation is greater that about 25xc2x0 C. In another preferred embodiment, the injection formation has a porosity greater than about 15%. In a particularly preferred embodiment, the injection formation is separated from the ground surface by one or more pairs of alternating layers of high permeability and low permeability.
In a preferred embodiment, the method further comprises monitoring pressure in the one or more than one of the alternating layers of high permeability and low permeability above the injection formation during a time selected from the group consisting of before biosolids injection, during biosolids injection, after biosolids injection and a combination of before biosolids injection, during biosolids injection and after biosolids injection. In a preferred embodiment, at least one low permeability layer of the one or more alternating layers of high permeability and low permeability comprises shale. In a particularly preferred embodiment, the one or more pairs of alternating layers of high permeability and low permeability is at least three pairs of alternating layers of high permeability and low permeability.
In a preferred embodiment, the degeneration of the biosolids generates a gas selected from the group consisting of carbon dioxide, sulfur dioxide, hydrogen sulfide and combinations of the preceding. In a particularly preferred embodiment, the method further comprises decreasing the rate of the generated carbon dioxide, sulfur dioxide, hydrogen sulfide or combination of the preceding by performing an action selected from the group consisting of blending at least one waste stream with the provided biosolids, inoculating the biosolids with at least one species of bacteria, changing the temperature of the biosolids, changing the salinity of the biosolids, adding at least one chemical to the biosolids and a combination of the preceding.
In a preferred embodiment, the method further comprises creating fractures within the injection formation before injecting the biosolids into the injection formation. In another preferred embodiment, the method further comprises transporting the selected biosolids to an injection site by pipe before injecting the biosolids. In a particularly preferred embodiment, the method further comprises monitoring pressure in the injection formation at a time selected from the group consisting of before injecting the biosolids into the injection formation, during the injection of the biosolids into the injection formation, after injecting the biosolids into the injection formation and a combination of the preceding.
In a preferred embodiment, the method further comprises increasing the rate of degradation of the biosolids by performing an action selected from the group consisting of blending at least one waste stream with the provided biosolids, inoculating the biosolids with at least one species of bacteria, changing the temperature of the biosolids, changing the salinity of the biosolids, adding at least one chemical to the biosolids and a combination of the preceding. In another preferred embodiment, the chemical added to the biosolids is potassium. In a particularly preferred embodiment, the method further comprises allowing methane to be generated by the degradation of the injected biosolids and recovering methane generated by the degradation of the injected biosolids, after injecting the biosolids into the injection formation. In a particularly preferred embodiment, the rate of methane generation is increased by performing an action selected from the group consisting of blending at least one waste stream with the provided biosolids, inoculating the biosolids with at least one species of bacteria, changing the temperature of the biosolids, changing the salinity of the biosolids, adding at least one chemical to the biosolids and a combination of the preceding. In another preferred embodiment, the chemical added to the biosolids is potassium.
In a preferred embodiment, the degradation of the biosolids generates a gas selected from the group consisting of carbon dioxide, sulfur dioxide, hydrogen sulfide and combinations of the preceding, and where the method further comprises decreasing the rate of the generated carbon dioxide, sulfur dioxide, hydrogen sulfide or combination of the preceding by performing an action selected from the group consisting of blending at least one waste stream with the provided biosolids, inoculating the biosolids with at least one species of bacteria, changing the temperature of the biosolids, changing the salinity of the biosolids, adding at least one chemical to the biosolids and a combination of the preceding. In another preferred embodiment, the chemical added to the biosolids is potassium.